Certain aspects of the present disclosure generally relate to the field of geophysical surveying and may have particular applicability to components used in marine settings.
Inversion is a widely used process for reconstructing geological properties of a subsurface structure from recorded energy emanations and reflections of the structure. The structure is modeled based on estimated geophysical properties, and the energy return is predicted and compared with real survey data to determine the accuracy of the estimated properties.
In order to understand properties of the materials and structures in the earth, a model is typically used to derive the properties from the recorded data. In the case of electromagnetic surveying, the recorded data are typically voltages, and these voltages, related to characteristics of the source radiation and the geometry of the source and receiver arrangement, indicate the transformation of the radiation by the structures and materials in the earth. The transformation, in turn, indicates physical properties of the materials such as resistivity, magnetic permeability, density, and other physical properties. Using a physical model that relates such physical properties to transformations in electromagnetic radiation, the physical parameters can be iteratively determined by computing results from the model based on a representation of the known source radiation, the geometry of the survey, and estimates of the physical properties. Agreement of the model results with the detected radiation indicates the accuracy of the estimate, and if such accuracy is inadequate, the estimate is refined until a desired accuracy is reached. This process is typically called inversion. The sub-process of calculating model results, as part of the inversion process, is typically referred to as “forward modeling”.
In a typical geophysical surveying process employing inversion, a large amount of data is collected over a wide geographical area. For purposes of inverting the data, the volume under the surveyed geographical area is represented as a “grid” or matrix of “cells”, each representing a small volume of the surveyed area. Each cell may be modeled as having uniform physical properties, so that one value of a physical property applies to the entire cell. The physical property is estimated, and the forward model is computed to give an estimate of the recorded data. The estimate is compared to the recorded data, and the quality of the fit is judged and compared to one or more criteria. If the quality of the fit is insufficient, the estimate of the physical property of each cell is adjusted, and the forward model recomputed. This iterative process continues until the fit criteria are met, at which point the inversion is said to have “converged”.
Computing the forward model of resistivity and computing an adjustment to the estimate are the two resource intensive parts of the inversion process. Techniques for reducing computational time and resource requirements of these two parts are needed.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one aspect may be beneficially utilized on other aspects without specific recitation.